For reasons lost, citizens petitioned the City of Petaluma to acquire a second plaza in 1873. $1,250 was appropriated towards the purchase of a city block bounded by D, E, 3rd and 4th Streets. (Weekly Argus, Nov. 14, 1873.) John McNear, a prominent local businessman, donated an additional $1,250. And thus begins the tale of a park that owes its existence and much of its appearance to volunteers and donors. Other Petaluma parks have also been shaped by benefactors, but none so much as this park, then called the D Street Plaza, or simply the Lower Plaza.
By 1876, Edward S. Lippitt, a local attorney who involved himself in many aspects of town life, provided a formal plan for the new park that contained several ornamental trees and shrubs, as well as pathways. It seems a plan to care for the new park was not developed, for the landscape failed. 100 walnut trees were planted as early as 1886, but again, with no plan for irrigation or maintenance, the plaza became derelict.
In 1896, the redoubtable women of the Ladies Improvement Club took matters into their own hands, dismayed at the condition of the two plazas in town. Walnut Park, as the second plaza was later named by the Ladies, emerged quickly under their care after some decades of previous and piecemeal improvements. Hrs. H. H. Atwater, a resourceful leader in town, championed this park. The Ladies raised funds for irrigation, pathways, and additional planting. The need for irrigation was acute, and funding for a well, tankhouse and windmill were provided through fundraisers in 1899. The Women's Temperance Union donated an elaborate fountain; it was later removed. The Ladies continued managing the park until around 1911 when a Parks Director position was created in the city.
The park was conceived as a formal space for strolling, consistent with popular Victorian ideas about public park uses that generally excluded active play and entertainment. Ideas began to change, and in 1927 a gazebo for community entertainment was built in the center of the park. Designed and constructed by the local Lions Club, it hosted weekly musical performances that were hugely popular. There were few benches in the park at that time, and those wealthy enough to own cars simply parked them around the perimeter of the park, parties honking their approval at the end of each musical piece. Several benches were added around the gazebo in 1929, for the benefit of those without cars.
In 1941, the windmill and tankhouse were replaced by a building designed by local star architect Brainerd Jones. The stucco building, feature a bas-relief squirrel, housed restrooms and a playroom. The first playground was likely built at the same time, a result of increasing interest in using parks for active play for children.
A plaque honoring locals who fought in the Vietnam War was installed near the gazebo. Stolen in 2013, townspeople quickly replaced it with a more substantial plaque. That same year an alliance of local service groups, led by Maureen Frances, raised around $150,000 for new park paving and other improvements. In October of 2016, the same coalition succeeded in converting the small building in the park into a police substation. The exterior was painted and the interior remodeled.